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From: M Powers on 24 Mar 2010 11:21
Hi,

I have some waveforms in MATLAB with a DC offset that I want to filter out. I based this filter off of a first order analog prototype but am getting unexpected results.

I assumed that the implicit periodicity of the DFT would cause the offset of the waveform in the code below to be a DC component. Instead, I get results that apparently treat the offset as a step response to the high pass filter. Is this an intrinsic limitation of the DFT? Advice is appreciated.

MATLAB code:

fs = 5e9;
t = -50e-9:1/fs:50e-9;
DCOffset = 0.5;
wfm = 0.5 * rectpuls(t,2e-9) + DCOffset;

%analog prototype
cutoffFreq = 1e6;
timeConst = 1 / (cutoffFreq * 2 * pi);
aNum = [timeConst 0];
aDen = [timeConst 1];
[dNum, dDen] = bilinear(aNum, aDen, fs);

fwfm = filter(dNum, dDen, wfm);
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